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In der vorliegenden Arbeit wurde die kohärente Vielteilchen-Quantendynamik von Ladungsträgern in Halbleitern in einem Regime nichtperturbativer Optik mit einer Zeitauflösung schneller als eine Lichtschwingung erforscht. Dabei gelingt es erstmals, ein kohärentes Landau-quantisiertes Elektronengas in Galliumarsenid auf ultrakurzen Zeitskalen nichtlinear zu kontrollieren. Des Weiteren wird mit atomar starken THz-Laserimpulsen im hochreinen Volumenmaterial eine extrem nichtperturbative Ladungsträgergeneration ausgelöst. Die gewonnenen Erkenntnisse liefern neue Einblicke in die mikroskopische Dynamik von Elektronen unter dem Einfluss starker THz-Lichtfelder., In the present work, the coherent many-body quantum dynamics of charge carriers in semiconductors in a regime of nonperturbative optics with a time resolution faster than a light oscillation was investigated. For the first time, it is possible to nonlinearly control a coherent Landau-quantized electron gas in gallium arsenide on ultrashort time scales. Furthermore, with atomically strong THz laser pulses in the high-purity bulk material, an extremely nonperturbative charge carrier generation is triggered. The findings provide new insights into the microscopic dynamics of electrons under the influence of strong THz light fields.

In solids, the high density of charged particles makes many-body interactions a pervasive principle governing optics and electronics(1-12). However, Walter Kohn found in 1961 that the cyclotron resonance of Landau-quantized electrons is independent of the seemingly inescapable Coulomb interaction between electrons(2). Although this surprising theorem has been exploited in sophisticated quantum phenomena(13-15), such as ultrastrong light-matter coupling(16), superradiance(17) and coherent control(18), the complete absence of nonlinearities excludes many intriguing possibilities, such as quantum-logic protocols(19). Here, we use intense terahertz pulses to drive the cyclotron response of a two-dimensional electron gas beyond the protective limits of Kohn's theorem. Anharmonic Landau ladder climbing and distinct terahertz four-and six-wave mixing signatures occur, which our theory links to dynamic Coulomb effects between electrons and the positively charged ion background. This new context for Kohn's theorem unveils previously inaccessible internal degrees of freedom of Landau electrons, opening up new realms of ultrafast quantum control for electrons.

This paper investigates persistence of Swiss consumer price inflation using aggregate and disaggregate inflation data covering 1983-2008. We document that persistence of sectoral inflation rates is below persistence of aggregate inflation. Our main finding is that inflation persistence significantly declines in the early 1990s. An estimated factor model reveals that inflation persistence stems from a persistent component that is common to inflation rates across sectors. Both the relevance and the persistence of the common component decline over time. Depending on the sample period and aggregation level, 70 to 90 percent of the variance in sectoral inflation rates is accounted for by short-lived sectoral factors.

This paper investigates the effects of media coverage and macroeconomic conditions on inflation forecast disagreement of German households and professional forecasters. We adopt a Bayesian learning model in which media coverage of inflation affects forecast disagreement by influencing information sets as well as predictor choice. Our empirical results show that disagreement of households depends on the content of news stories (tone) but is unaffected by reporting intensity (volume) and by the heterogeneity of story content (information entropy). Disagreement of professionals does not depend on media coverage. With respect to the influence of macroeconomic variables we provide evidence that disagreement of households and professionals primarily depends on the current rate of inflation., KOF Working Papers, 223

This paper assesses the probability method for quantifying EU consumer survey data on perceived and expected inflation. Based on micro-data from the Swedish consumer survey that asks for both qualitative and quantitative responses, I find that the theoretical assumptions of the method do not hold. In particular, estimated models of response behavior indicate that qualitative inflation expectations are not ordered. Nevertheless, the probability method generates series that are highly correlated with the mean of actual quantitative beliefs. For quantifying the cross-sectional dispersion of beliefs, however, an index of qualitative variation outperforms the probability method., KOF Working Papers, 230

This paper investigates how households form their perceptions of consumer price inflation. Using data from the harmonized EU consumer survey, we find that inflation perceptions are inefficient and highly heterogeneous, yet contemporaneously related to the actual rate of inflation. Consequently, we estimate how often households update their beliefs employing Carroll's (2003) epidemiological model. Our results indicate that inflation perceptions are generally less responsive to new information than expectations. Unlike studies on expectations, we cannot confirm that a constant fraction of the population updates information every month. Also, the cross-sectional heterogeneity of perceptions is higher than implied by infrequent updating alone., KOF Working Papers, 204

This paper investigates how economic conditions are associated with age-sex group specific suicide rates in a panel of 28 OECD countries over the period 1980-2002. We consider the trend and cyclical components of income, unemployment, income inequality, inflation, as well as various socio-demographic control variables. Results depend on whether stationarity properties are adequately accommodated or not. Estimating models in first differences we find that the cyclical component of income is negatively associated with suicide rates of men, while suicide rates of women are primarily affected by unemployment. Moreover, our estimations show that the effects of the cyclical component of income and unemployment are most pronounced in OECD countries with low public social security spending., KOF Working Papers, 207

This paper investigates how households form their perceptions of consumer price inflation. Using data from the harmonized EU consumer survey, we find that inflation perceptions are inefficient and highly heterogeneous, yet contemporaneously related to the actual rate of inflation. Consequently, we estimate how often households update their beliefs employing Carroll's (2003) epidemiological model. Our results indicate that inflation perceptions are generally less responsive to new information than expectations. Unlike studies on expectations, we cannot confirm that a constant fraction of the population updates information every month. Also, the cross-sectional heterogeneity of perceptions is higher than implied by infrequent updating alone.

erahertz near fields of gold metamaterials resonant at a frequency of 0.88 THz allow us to enter an extreme limit of nonperturbative ultrafast terahertz electronics: Fields reaching a ponderomotive energy in the keV range are exploited to drive nondestructive, quasistatic interband tunneling and impact ionization in undoped bulk GaAs, injecting electron-hole plasmas with densities in excess of 1019 cm−3. This process causes bright luminescence at energies up to 0.5 eV above the band gap and induces a complete switch-off of the metamaterial resonance accompanied by self-amplitude-modulation of transmitted few-cycle terahertz transients. Our results pave the way towards highly nonlinear terahertz optics and optoelectronic nanocircuitry with subpicosecond switching times.